A cooling heat exchanger such as a cold trap is typically used in vacuum systems to remove gases having a relatively high temperature of solidification, or sometimes liquefaction, from a gas with a lower temperature of solidification. Generally, gaseous or particulate contaminants are removed from a vapor stream flowing through the cold trap. For example, a cold trap is often used to remove aluminum chloride in a reactive ion etching system.
A cold trap captures contaminants by providing a cold surface in the flow path of the particle. Particles which strike the cold surface are immobilized by freezing onto or by adsorption into the cold surface. To insure that all of the contaminants collide with the cold surface, chevrons or simple baffle arrangements are used for obstructing the traveling path.
In order to create a cold surface or cold region sufficient to trap contaminant gases, cryogenic temperatures are needed. Typically, a coolant such as liquid nitrogen or a dry-ice-acetone mixture is placed in contact with the region that is to be cooled. Using these types of coolants, however, require special hardware for circulating or replenishing the liquid coolant.
For an efficient cooling system the coolant is insulated to prevent heat transfer to the ambient enclosure. Conventionally, a vacuum chamber surrounding the coolant is used for insulation. This, however, adds hardware to the system to create the vacuum as well as a concern for leaks in the vacuum chamber. Such systems can be expensive and cumbersome.
Therefore, there is a need for a cold trap which can be used to remove contaminants more efficiently, economically, and conveniently.